Various devices for inspecting containers are known from the state of the art, especially in the field of the beverage industry. These devices inspect the outside wall or the mouth of the containers, for example, for defects. However, it is also necessary to inspect not only the containers themselves but also their closures for defects. For example, it is possible for such container closures to have a cross section that deviates from a certain target cross section, e.g., a circular cross section. It is also possible that a securing ring which is usually provided on such containers might be damaged.
However, inspection of container closures is associated with a number of problems. First, the container closures have a wide variety of colors, ranging from white to colors such as red, green or even black. This makes an optical inspection difficult because the corresponding container closures reflect light in different intensities. In addition, on the inside, such container closures often have protective films, e.g., made of aluminum, which strongly reflect light and thus make observation difficult.
U.S. Pat. No. 4,924,107 describes such a device for inspecting the inside surfaces of a container. This device has a camera, which observes the inside surface of a container. In addition, an illumination means is also provided for illuminating the interior space of the object.
This device operates satisfactorily for containers but it is not suitable for container closures of different colors because the reflection that occurs in observation cannot be adequately suppressed.
DE 19 852 369 C1 describes a device and a method for testing cylindrical test objects. In this method, a light is passed through the objects to be inspected and a transmission image of the test objects is recorded with the help of a camera. However, this device is not suitable for objects that are not transparent, such as the nontransparent container closures to be inspected.